Intel Xeon D 1521 's Advantages
Released 2 years and 5 months late
More modern manufacturing process (14nm vs 22nm)
Lower TDP (45W vs 65W)
Intel Xeon E3 1285L v3 's Advantages
Higher base frequency (3.1GHz vs 2.4GHz)
Larger L3 cache size (8MB vs 1.5MB)